1. Advanced LIGO Status Report
Gregory Harry
LIGO/MIT
On behalf of the LIGO Science Collaboration
22 September 2005
ESF PESC Exploratory Workshop – Perugia Italy
LIGO-G R

2. Advanced LIGO Overview
LIGO infrastructure designed for a progression of instruments
Nominal 30 year lifetime
Initial LIGO planned (and required) to run at design sensitivity for 1 integrated year
Will begin end of 2005
10 Hz
100 Hz
1 kHz
10-22
10-23
10-24
10-21
Initial LIGO
Advanced LIGO
Second generation interferometer
Quantum noise limited in much of band
Signal recycling mirror for tuned response
Thermal noise in most sensitive region
About factor of 10 better sensitivity
Sensitive band down to ~ 10 Hz
Detect neutron star inspirals out to about
200 Mpc 2

3. Advanced LIGO Subsystems
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 3

4. Prestabilized Laser 40 KG SAPPHIRE OR FUSED SILICA TEST MASSES
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 4

5. Prestabilized Laser End-pumped Nd:YAG rod injection locked
Backup efforts in slabs & fiber lasers
Frequency stabilization
10 Hz/Hz1/2 at 10 Hz required (10 Hz/Hz1/2 at 12 Hz seen in initial LIGO)
Intensity stabilization to 2x10-9 ΔP/P at 10 Hz required
Development at Max-Planck Hannover, Laser Zentrum Hannover
Max Planck has granted funds for delivery of all PSLs
Continued work on the mode shape of 200 W laser 5

6. Input Optics 40 KG SAPPHIRE OR FUSED SILICA TEST MASSES
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 6

7. Input Optics Design similar to initial LIGO 20X higher power
Electo-optic modulators undamaged by 85 W for 400 hours
Mach-Zehnder modulation system
Eliminates sidebands on sidebands
Theoretical investigations of noise
Prototype developed
Faraday Isolator
20 mm aperture with thermal lensing & depolarization compensation
Adaptive Mode Matching Telescope
Silica optics with CO2 laser heating
Modeling indicates 1 ppm loss tolerable in mode cleaner 7

8. Seismic Isolation 40 KG SAPPHIRE OR FUSED SILICA TEST MASSES
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 8

9. Seismic Isolation Choose an active approach for BSC
High-gain servo systems, two stages of 6 degree-of-freedom each
External hydraulic actuator pre-isolator
Extensive tuning of system after installation
HAM design being reviewed
Stanford prototype is baseline
Studying single-stage system for lower cost & complexity
External hydraulic pre-isolator
installed on initial LIGO (Livingston)
Increases initial LIGO duty cycle
Exceeds advanced LIGO requirements 9

10. Suspensions 40 KG SAPPHIRE OR FUSED SILICA TEST MASSES
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 10

11. Suspensions Adopt GEO 600 silica suspension design
Multi-stage suspension, final stage fused silica
Ribbons baseline design, fibers as fallback
Quadruple pendulum design chosen
Ribbons silicate bonded to test mass
Leaf springs (VIRGO origin) for vertical compliance
PPARC funding approved for Adv LIGO (2003)
Significant financial, technical contribution; quad suspensions, electronics & some substrates
Quad lead in UK U Glasgow, Birmingham, Rutherford
Mode Cleaner (triple) control prototype in LASTI
Performance as expected, some model improvements
Quad control prototype delivered this Fall
Laser fiber/ribbon drawing apparatus developed
Welds being characterized for strength/Q etc.
No problems seen 11

12. Core Optics 40 KG SAPPHIRE OR FUSED SILICA TEST MASSES
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 12

13. Mechanical Loss in Fused Silica
Core Optics
Silica chosen as substrate material
Improved thermal noise performance from original anticipation
Some concerns about unknowns with sapphire
Coatings dominate thermal noise & optical absorption
Progress reducing f with doping
See talk by Sheila Rowan
Mechanical Loss in Fused Silica
Parametric instability being studied
May have to spoil modal Q’s of optics
Other issues
Thermal compensation works on initial LIGO (see previous talk)
Noise effects of charging under investigation
Mechanical mode kHz
Optical mode
Overlap 0.8 13

14. Readout 40 KG SAPPHIRE OR FUSED SILICA TEST MASSES ACTIVE ISOLATION
180 W LASER, MODULATION SYSTEM
40 KG SAPPHIRE
OR FUSED SILICA TEST MASSES
ACTIVE ISOLATION
QUAD SILICA SUSPENSION
PRM Power Recycling Mirror
BS Beam Splitter
ITM Input Test Mass
ETM End Test Mass
SRM Signal Recycling Mirror
PD Photodiode 14

15. Readout DC rather than RF sensing
Dual recycled (signal & power) Michelson with Fabry-Perot arms
Offers flexibility in instrument response
Can provide narrowband sensitivity
Critical advantage: can distribute optical power in interferometer as desired
Output mode cleaner
DC rather than RF sensing
Offset ~ 1 pm at interferometer dark fringe
Best signal-to-noise ratio
Simplifies laser, photodetection requirements
Perfect overlap between signal & local oscillator
Easier to upgrade to quantum non- demolition in future 15

16. Prototypes - I LASTI (LIGO Advanced System Test Interferometer) – MIT
Test full scale components
Verify installation
Explore seismic/low frequency noise
Already used for initial LIGO – HEPI
Triple control suspension prototype installed
Quad control suspension prototype this Fall
LASTI - MIT
40 m Interferometer - Caltech
Sensing/controls tests of readout
Locking of dual recycled interferometer
Engineering model for data acquisition, software, electronics
Exploring modulation techniques
Mach-Zehnder design
40 m - Caltech 16

17. Prototypes - II Engineering Test Facility - Stanford
Seismic isolation prototype
1000x Isolation demonstrated
1-10 Hz performance in progress
ETF - Stanford
Gingin – Western Australia
High power tests
Thermal lens compensation
Hartmann wavefront sensor
Parametric instability tests
Mexican Hat Mirrors – CIT
Reduce thermal noise
Seeing higher order modes in agreement with theory
TNI Results
Thermal Noise Interferometer – CIT
Silica/tantala Brownian noise
Sapphire thermoelastic noise
Silica/titania-doped tantala Brownian noise -- in progress 17

18. Advanced LIGO Project Status
National Science Board (NSB) endorsed Advanced LIGO proposal in October 2004
Contingent upon integrated year of observation with Initial LIGO
National Science Foundation & Presidential Budget includes LIGO
One of 3 new projects to start in next 3 years
October 2007 start date
Shut down first initial LIGO interferometer mid 2010
Finish installing 3rd interferometer end 2013
Review of costs, manpower & schedule complete in 2005
Fresh analysisupdates of technology
Current best estimates comparable with NSB-approved costs 18

19. Conclusions Advanced LIGO will have ~ 10 X sensitivity of initial LIGO
1000 X rate for homogeneously distributed sources
Seismic isolation down to near 10 Hz
Laser will have ~ 200 W of power
Fused silica ribbon suspensions
Fused silica substrates for core optics
Coating crucial and still under development
DC readout of dual-recycled configuration
Prototypes in place or under development for most noise sources and/or areas of concern
Budget situation hopeful for 2007 start
No check in hand yet 19

20. Contact Information
Gregory Harry 20